Boom-Bust Cycles Constrain Host-Parasite Dynamics, Suppress Parasite Spread, and Drive Parasites Extinct.

AbstractHost-parasite theory is rooted in equilibrium dynamics. However, many host species exhibit "boom-bust" life histories or range expansions characterized by population booms and severe bottlenecks. The dynamic host density in boom-bust systems may disrupt the interactions between density-dependent processes such as parasite transmission and birth, resulting in unique dynamics compared with a host population at equilibrium. We subjected a simple compartment model to recurring host bottlenecks to approximate a boom-bust life history. We found that recurring bottlenecks suppressed disease spread by giving the host population an opportunity postbottleneck to expand faster than the disease could spread. As bottlenecks became more frequent and/or severe, disease spread was suppressed to such low levels that parasite extinction was virtually guaranteed. We found that our model was conservative and presented a near-best-case scenario for the parasite. Our results indicate that the dynamic host density of boom-bust systems creates new system behaviors that are not seen in equilibrium models. Additionally, we argue that our results generalize to any horizontally transmitted symbiont, including mutualists and commensals. We conclude that boom-bust dynamics must be explicitly modeled to accurately predict disease spread and the resulting evolutionary dynamics in hosts and their symbionts.